// streams/OptionalMap.java
// (c)2017 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.

import java.util.Arrays;
import java.util.function.Function;
import java.util.stream.Stream;

class OptionalMap {
    static String[] elements = {"12", "", "23", "45"};

    static Stream<String> testStream() {
        return Arrays.stream(elements);
    }

    static void
    test(String descr, Function<String, String> func) {
        System.out.println(" ---( " + descr + " )---");
        for (int i = 0; i <= elements.length; i++) {
            System.out.println(
                    testStream()
                            .skip(i)
                            .findFirst() // Produces an Optional
                            .map(func));
        }
    }

    public static void main(String[] args) {

        // If Optional is not empty, map() first extracts
        // the contents which it then passes
        // to the function:

        test("Add brackets", s -> "[" + s + "]");

        test("Increment", s -> {
            try {
                return Integer.parseInt(s) + 1 + "";
            } catch (NumberFormatException e) {
                return s;
            }
        });

        test("Replace", s -> s.replace("2", "9"));

        test("Take last digit", s -> s.length() > 0 ?
                s.charAt(s.length() - 1) + "" : s);
    }
    // After the function is finished, map() wraps the
    // result in an Optional before returning it:
}
/* Output:
 ---( Add brackets )---
Optional[[12]]
Optional[[]]
Optional[[23]]
Optional[[45]]
Optional.empty
 ---( Increment )---
Optional[13]
Optional[]
Optional[24]
Optional[46]
Optional.empty
 ---( Replace )---
Optional[19]
Optional[]
Optional[93]
Optional[45]
Optional.empty
 ---( Take last digit )---
Optional[2]
Optional[]
Optional[3]
Optional[5]
Optional.empty
*/
